Researchers have described a new species of crocodilian from the Late Jurassic of Chile. Named Burkesuchus (B. mallingrandensis), it heralds from the Toqui Formation of southern Chile. As such, this 70-centimetre-long reptile shared its home with sauropods and the bizarre Chilesaurus (C. diegosuarezi). Analysis of the fragmentary fossil bones, including all important skull material suggests that Burkesuchus was a basal member of the Mesoeucrocodylia, the crocodilian lineage that led to modern crocodiles.

Burkesuchus fossil remains and fossil location.
A map (insert) showing the location of the fossil finds, the geology of the region and a silhouette of Burkesuchus showing location of known bones within the skeleton with a human hand silhouette to show scale. Picture credit: Novas et al.

Shedding Light on the Fauna Associated with the Toqui Formation

Fossils of Burkesuchus were collected from outcrops of the Toqui Formation (Tithonian stage of the Late Jurassic). Analysis of zircon samples subjected to radiometric dating suggest that this small crocodilian lived around 147 million years ago. The fossils found consist of skull material, dorsal vertebrae, elements from the limbs including a right scapula and coracoid (shoulder bones) a nearly complete right femur (thigh bone) and several osteoderms (body armour).

Burkesuchus skull material and explanatory line drawings.
Photographs and line drawings of the cranium (SGO.PV 17700) of Burkesuchus mallingrandensis in (A, B) dorsal; (C, D) posterior; and (E, F) left lateral views. Note scale bar equals 1 cm. Picture credit: Novas et al.

A “Missing Link” in Crocodile Evolution

The genus name honours the American Coleman Burke for his financial support of the field work and “suchus” from Latin, meaning crocodile. The species name is a reference to Mallín Grande, the name given to this scenic, very beautiful but remote part of Chile, south of General Carrera Lake.

Semi-aquatic crocodilian fossils dating from the Jurassic of South America are rare. To date, the only other non-marine crocodilian known from this continent is Batrachomimus from the Upper Jurassic of Brazil, which is thought to be a paralligatorid. However, analysis of the limb bones associated with Burkesuchus reveals that it possibly represents an intermediate form between crocodilians with a more semi-erect gait and sprawling forms reflecting the gait and locomotion of modern crocodilians. Burkesuchus could represent a transitional form, helping palaeontologists to understand the evolutionary history of this important group of archosaurs.

Modern crocodile compared to Kaprosuchus
Comparing the gait of a modern crocodile (top) with that of Kaprosuchus from the Late Cretaceous of Niger. During the Mesozoic crocodyliforms occupied a wide variety of ecological niches and many different gaits were adopted. Today, modern extant crocodilians and their relatives all have a sprawling gait.

The discovery of Burkesuchus expands the meagre record of non-marine crocodile representatives from the Late Jurassic of South America and the researchers conclude that Batrachomimus and Burkesuchus indicate that the evolution of more derived crocodyliforms could have occurred in South America.

Photographs of dorsal vertebrae and an osteoderm of Burkesuchus.
Photographs of vertebrae and osteoderm of Burkesuchus mallingrandensis (SGO.PV 17700). (A) cervical vertebra in left lateral view; (B–D) dorsal vertebra in (B) dorsal, (C) anterior, and (D) left lateral views; (E–F), dorsal osteoderm in (E), dorsal and (F), ventral views. Scale bar equals 1 cm. Picture credit: Novas et al.

The scientific paper: “New transitional fossil from late Jurassic of Chile sheds light on the origin of modern crocodiles” by Fernando E. Novas, Federico L. Agnolin, Gabriel L. Lio, Sebastián Rozadilla, Manuel Suárez, Rita de la Cruz, Ismar de Souza Carvalho, David Rubilar-Rogers and Marcelo P. Isasi published in Scientific Reports.